 NGC
1931 is a tiny little cluster of stars embedded in
nebulosity found about a degree to the west of the open
cluster M36. At the heart of the NGC 1931 cluster lies
a tiny version of the famous Trapezium in M42; four stars
that make a rough trapezoid.
This is a small
object, so be sure to try as much magnification as the
conditions will bear on it. In smaller scopes or at
low powers it will appear as a fuzzy star. More
magnification will reveal a fairly bright, round fuzzy knot
of nebulosity. OIII and H-Beta filters have little
effect on the nebula.
Brian Skiff
gathered some information regarding the trapezium stars,
which I have reproduced below. The multiple star
system that forms the "little trapezium" is ADS
4112 (BD+34 1074).
|
| Pair |
Mag |
Sep |
PA° |
| AB |
11.5,12.3 |
8.1" |
239 |
| AC |
13.0 |
10.5" |
310 |
| AE |
14.0 |
14.6" |
17 |
| BD |
~15.8 |
2.3" |
322 |
|
| Comp |
R.A. |
Dec. |
| A |
5h31m27.08s |
+34°14'49.6" |
| B |
5h31m26.54s |
+34°14'45.0" |
| C |
5h31m26.43s |
+34°14'56.3" |
| E |
5h31m27.50s |
+34°15'03.2" |
|
The A, B, and C stars
are easy to see but the E component is a little more difficult.
At least an 8-inch scope will be required to see it. The D
component is even more difficult, requiring a very large aperture.
When I observed NGC
1931 in my 18-inch f/4.5 I immediately noticed the nebula as a
bright knot at 97x. I was surprised at how bright it appeared.
The best view came at 430x, where the little trapezium became very
obvious.
The field in an 8-inch f/6 at
50x. North is down and east is to the right.
|
